Conventional disk drives utilize a record unit including a disk of flexible material rotatably carried in a jacket and coated on both faces with a magnetic material, yet information in the form of magnetic signals can be written on or read from only one face of the disk because the record unit has no means to permit it to be used in an inverted or reversed position relative to the read-write head of the disk drive. Typically, the record unit has a configuration which renders it compatible with a particular disk drive. There are several U.S. companies which market disk drives; thus, there are several different record unit configurations commercially available at the present time.
The particular means on the jacket and disk of a conventional record unit include a single group of aligned holes through the jacket and the disk for use with a disk rotation sensor, a single slot for use with the read-write head, and possibly a notch or hole in the jacket to provide a write enable function for the corresponding disk drive. The record unit can only be coupled to the disk drive in one way because of the irregular positioning of the hole and notch sensors of the disk drive.